The element that has the largest atomic radius is cesium. It has an atomic radius of 298 pm, or picometers. An alkali metal, cesium is so active that it instantly explodes if dropped into cold water. It's also one of the few metals that becomes a liquid at close to room temperature. Its melting point is 83.19 degrees Fahrenheit.
One of cesium's most important functions is as the basis for the atomic clock. Cesium is used to calculate the length of a second. This is done by beaming a signal of a certain frequency through isolated cesium atoms.
Cesium is also used as a "getter," which means that it will remove any trace of oxygen or water from a vacuum tube. It's also used in oil well drilling to clear any leftover chips of rock. Cesium has also been used to sterilize surgical equipment, food and sewage.
Cesium is a fairly rare element on earth, but it's more abundant than silver, mercury or even tin. It's most often found in pegmatite ores. One of the richest sources of this ore is in Manitoba, Canada.
The atomic number of cesium is 55. Its atomic weight is 132.90545, and its density is 1.879.